The continued development of inbred and serologically characterized rabbits is combined with the study of antigens of the erythrocytes, tissue cells and serum proteins of the rabbit. Our transplantation studies are directed towards recognizing the alleles at the major histocompatibiliy locus (RL-A) and the detection of response to incompatibility at minor loci. We are also interested in the genes, linked to RL-A, controlling the mixed lymphocyte reactions and the immune response to natural antigens. Blood group antigens with unusual modes of inheritance such as the interaction antigen, are being used as models for the sdudy of interallic interactions. The histocompatibility gene characterized rabbits are used for study of the graft rejection reaction particularly the early recognition of potential for hyperacute rejection.